This invention relates to a distributor device for improving the distribution and mixing of gas and liquid in the region between catalyst beds in downflow catalytic reactors comprising a plurality of said beds. More particularly, the invention relates to a distributor device for improving the distribution and mixing of gas and liquid entering the final distributor plate above the top of a succeeding catalyst bed. The distributor device is particularly suitable for catalytic reactors in which gas-liquid mixtures are passed through beds of solid catalyst particles, particularly for downflow catalytic reactors used for hydrotreating and hydrocracking in oil refining operations.
In downflow reactors it is necessary that gas and liquid are properly mixed across the horizontal cross section of the reactor prior to entering the catalyst beds. A plurality of catalyst beds is arranged within the reactor and a distributor system for the proper mixing of gas and liquids is arranged in the region between two subsequent catalyst beds. This region is normally provided with a gas injection line underneath a catalyst bed, whereby additional gas is injected to compensate for the gas already been consumed in the previous catalyst bed or as a quench gas, for instance by injection of hydrogen. The liquid falling downward from the above-lying catalyst bed is allowed to accumulate by means of a plurality of spillways located in a collector tray and positioned below or above the level of the gas injection line. After reaching a certain level, the liquid passes through the spillways into a mixing chamber where a swirling movement of the liquid is provided. This enables good mixing of the liquid and thereby even temperature conditions of the liquid. The liquid from the mixed chamber falls downward onto a deflector or impingement plate, whereby the flow is redirected onto a first distributor tray having a large number of downflow openings for the passage of liquid. In this tray a rough distribution of the gas and liquid across the reactor is effected. A pool of liquid accumulates in this tray and covers the openings so that the passage of gas is precluded. The passage of gas from said first distributor tray is enabled by the provision of a number of chimneys. The two phases are then mixed downstream in a second or final distributor tray having a number of tubular downcomers for the flow of gas and liquid. This tray is dedicated to redistribute the gas and liquid substantially symmetrically across the horizontal cross section of the reactor over the top of the subsequent catalyst bed.
In order to improve the uniformity of distribution and mixing of vapour and liquid across the reactor U.S. Pat. No. 4,836,989 describes a distributor system in the region between catalyst beds as described above, in which the outlets of the spillways are adapted to impart a swirling motion to the liquid as this enters the mixing chamber. Each of the chimneys for the downward passage of vapour connected to the first distributor tray comprises an open-topped tube extending above said first distributor tray and includes an apertured plate at its lower end. The high velocity and swirling motion prevailing in the mixing chamber manifests itself in the chimneys downstream and as a result the flow leaving the chimney will experience a greater flow velocity towards the reactor wall than towards the center of the reactor. Accordingly, the downward flow from the chimneys is unevenly distributed in the second (final) distributor tray, with the attendant effect that the gas and liquid are not optimally mixed across the horizontal cross section of the reactor when contacting the underlying catalyst bed.